Some office shredders on the market use low-efficiency knives and parts, which have low crushing levels and unsatisfactory crushing effects, and cannot achieve the purpose of complete privacy protection. In order to make the improved shredder quickly occupy the market, it needs to be modified. The variant design of the product is a kind of parameter modification or partial adjustment of the structure of the product, or both, while keeping the basic function, structure and principle of the product unchanged [1]. Experts and scholars have proposed modular variant design [2], case-based reasoning variant design [3, 4], variant design based on variable and parameterized design methods [5] and so on. Variant design includes structural variants and parametric variants. Among them: structural variants are to modify the local structure of components to meet the design requirements; parametric variants are to modify the size parameters of the parameterized model to meet the design requirements [6]. Both variant designs have their advantages and disadvantages. If the parameters and size modifications cannot meet the ever-changing market demands, more creative thinking needs to be integrated into the structural variants. Literature [7] believes that in the absence of relevant experience and templates, experts rely more on design experience in structural variant design. At this time, the evolutionary route in the invention problem solving theory can be introduced to guide structural variants.

The evolutionary tree consists of the integration of evolutionary routes established according to certain objective trends [8]. It distributes the main implementation schemes of system components in a logical order. Both are designed and improved on the basis of existing products and have commonality. In this paper, by analogy analysis of successful cases of previous variant design and evolution tree improvement, the way of combining evolution tree and variant design is proposed. At the same time, an example knowledge base is introduced as a variant design case support to construct a product variant design process based on evolution tree. To guide the variant design of the shredder cutter.